Mining machines (see U.S. Pat. No. 4,278,293 and the art referred to therein and German Patent Documents Nos. 28 47 909 and 29 43 476) are frequently provided with elongated rotary excavators which are thrust against the face of the tunnel to be advanced or from which mineral matter is to be removed in a direction transverse to the axis of rotation of the excavator which can be provided with a conveyor flight and picks or other tools for eating away the face.
In a coal excavation, the excavator is referred to as a coal auger although similar excavators can be used for recovering other mineral matter from mine tunnels or for advancing a tunnel in a substratum.
It is known to provide such machines with a spraying system or to otherwise spray a liquid upon the rotating excavator so that the dust is dampened and poses less of a danger to moving parts of the machine, is less of a hazard to mine workers and the danger of explosion is minimized.
Machines for this purpose have included nozzles through which a liquid, generally water, was sprayed and which were continuously supplied with water delivered to the rotating member so that the spray was directed not only at the face or region of attack of the tools upon the mineral matter, but also in other directions including rearwardly and downwardly.
The result has been an undesirable wetting of excavated material which has caused compaction and difficulties in removing the excavated material from the tunnel front and has increased the complexity of processing the material, for example, in air classifiers or the like.
It has been proposed to provide the picks forming the tools of an excavating machine directly with respective nozzles and to additionally provide each nozzle with a valve actuated by relative movement of the pick and the excavator body carrying same so that the spray could be confined to the region at which the pick was actually in contact with a rock or coal face. Experience with such machines has shown, however, that they are unreliable and prone to breakdown, while being functionally deficient in the sense that the valve tend to remain open or to close at the wrong times.